( 390 ) 



plates taken at anothei- lime. With several lines the intensity too 

 appeared to he variahle. 



Jewell explaijis tliese [)henoniena on eertain hypotheses on densitv, 

 pressure and tenii)erature of tlie ahsitrhinu' and eniittinu- uases in the 

 ditVereiit lavers of the solar atmosphere, and l>y varial»le aseendinji; 

 and descending- \eloeities of matter. 



Hat,I'','.s iihnviiiKil solar sjn-cIfKm. 



Mneii greater than the iiregulai'ities mentiojied are those, found in 

 an "abnormaF' solar spectrum, lately deserihcd hy (i. E. Hale. ^) 



This highly remarkahle s|)ectriini had accidentally heen | (holographed 

 as long ago as February 1(S94 in a series of exposures made \\ith 

 the sole intention of inxestigating the peculiarities of tiu' grating. 

 ()jdy a few months later it was discovered that a vei-y extraordinary 

 phenomenou had i)eeii j)hotogra|iht'd. IIai.k hesitated to puMish this 

 accidental discovery. Copies of the plate were sent to several sj)ectro- 

 sco})i.sts for examinatioji with the re^piest that an explanation, referring 

 the phenomenon to some origin other than solar, might he su|»plied, 

 if possible. As no such explanation was foi'thcoming. the s|»ecti'a 

 were very carefully lucasui-ed and desci'ibed. 



On one and the same ]»late 12 ex|)osures had been successively 

 made in the third order >pectiiim of a plane grating. A solar image 

 of 51 u'.ui. in diameter w a> so adjusted that the iuiage of a sjtot 

 fell exactly tui the slit. The length of the slit (i).5 m.ui.i correspontled 

 to about one eightii of the suu"> diameter. 



The lirst e\[)osures show the normal >|ieclrum without any con- 

 siderable changes. Then came the disturbam-e. which ciilnujiated in 

 the eighth spectrum and. in the following h)ur, decreased rapidly. 

 Hai,e gives repi-oductions of four s|)ectra, each of them extending 

 from ;. 3812 to / 4132. N". 1 has been taken befoi-e the disturbance 

 occurred ; X". 2 is the most abnormal spectrum ; X". 3 is called 

 by Hat,e the "intennediate" s]>ectrum, it has been obtained a few- 

 moments after the abnormal one : X". 4 slio\vs once more the nor- 

 mal solar spectrum, as it was [»h(»tograi)hed at ajiother time on 

 another |)late. Xos. 1, 2 and 3 show a dark baud throughout the 

 whole spectrum, coi'i-e>poiidiiig to the sun-spot which had been 

 focused oJi the slit. 



The most ])rominent features of the abnormal sj)eclrnm are : 



1". The band due to the spot appears much fainter than in the 

 spectra, photographed before and after the disturbance. 



1) George E. Hale. "Solar research at llie Yerkes Ubservatory"', Aslro])li. .louin. 

 XVI p. 211-233, 1902. 



